The present invention relates to a device for emitting digital video images.
Although not exclusively, such a device comprising picture-taking means of the video camera type is intended more particularly to be mounted on an aircraft, especially a civil transport airplane, so as to produces images of the environment outside the aircraft and in particular of the environment fore and/or aft of the latter, which images are transmitted on a screen visible to a pilot of the aircraft.
Such a device allows, in particular, the pilot:
to have real-time vision of the positioning of the aircraft with respect to its environment on the ground; and
to aid the guidance of the aircraft, in particular when the latter is taxiing on a runway of an airport before takeoff or after landing, thus making it possible, despite the reduced handlability of the aircraft on the ground, to avoid a departure from the runway and in particular a departure of the rear wheels.
It is preferable to use digital images for this purpose. This is because it is known that digital images are not sensitive to interference, thereby engendering increased quality and increased reliability as compared with standard analog images. Moreover, digital images may be processed directly much more simply than analog images.
However, the generating of digital video images has a significant drawback: the risk of image freeze, that is to say the risk of continuous screening of the same image rather than of nonidentical successive images.
The origin of this image freeze may be a problem with one of the various steps (generation, storage, display, etc.,) for acquiring and processing the images and generally results from a defective zeroing of a video memory. This risk is accentuated by the ever greater complexity of video image emission devices, which may in particular implement varied and complex processing operations, such as image compression or the generation of xe2x80x9cmosaicsxe2x80x9d from several video sources.
Image freeze may have unfortunate consequences, especially in the aforesaid example, relating to the guidance of an airplane on the ground, since, the successive images generally not exhibiting significant differences, the pilot has difficulty in distinguishing between a motionless image and a frozen image, and this may induce him to make guidance errors.
Various solutions to detecting image freeze are known.
A first solution consists in erasing on each occasion the video memories between two successive images. However, this solution requires erasure logic with accurate time references so that the erasure can be carried out at the appropriate moment. Moreover, such logic has to be provided for each of the various video memories of the image emission device.
A second solution consists in comparing on each occasion two successive images. However, this solution requires duplication of the video memories so as to be able to preserve two successive images and moreover the provision of a comparator and associated processing logic. Moreover, in the case where the scene filmed is actually stationary, it is possible to have two identical consecutive images, so that this second solution then leads to erroneous detection of image freeze.
Consequently, none of these known solutions is satisfactory, all the more so since in the case of the aforesaid application to the guidance of an aircraft on the ground, with visual restoration fore and/or aft of the aircraft, these standard solutions render the on-board system more complicated and/less reliable.
The object of the present invention is to remedy these drawbacks. It relates to a device for emitting digital video images making it possible to detect any image freeze simply and reliably.
For this purpose, according to the invention, said device for emitting digital video images, comprising picture-taking means, is noteworthy in that it furthermore comprises means for forming at least one signal in the field of vision of said picture-taking means, so that said signal appears in at least some of the images produced by said picture-taking means, and in that said signal is formed in such a way as to vary temporally.
Thus, by virtue of the invention, while the signal is varying in the restored images, one is aware that normal unreeling of successive video images is occurring. On the other hand, as soon as said signal remains identical (and possibly absent) for a determined duration, the existence of a frozen image is detected.
The device in accordance with the invention thus makes it possible to detect visually, in a simple and reliable manner, any image freeze.
Furthermore, advantageously:
said signal is an intermittent signal, that is to say a signal which disappears and reappears at regular time intervals; and/or
said signal is formed in such a way as to appear at variable locations and/or in variable shapes in successive images produced by said picture-taking means.
Moreover, advantageously, said signal is formed in such a way as to appear, on each occasion, in a zone of the image, for example a corner of the image, where it does not impede the visual restoration of the scene represented in said image.
Said means for forming at least one signal may be incorporated into said picture-taking means. In this case, they are preferably miniaturized.
However, preferably, for safety, said means for forming at least one signal are exterior to said picture-taking means and independent of the latter. Thus, they are completely decoupled from said picture-taking means.
In an exemplary embodiment, said means for forming at least one signal may then comprise:
a generator of light pulses; and
an optical fiber linked to said generator of light pulses and arranged in such a way as to transmit in the field of vision of said picture-taking means the light pulses emitted by said generator of light pulses and representing said signal.
They may also, as a variant, comprise:
an element able to be moved in the field of vision of the picture-taking means; and
a means of moving said element, said element being moved in such a way as to appear intermittently, and possibly at variable locations, in successive images produced by said picture-taking means and to represent said signal.